We have continued to study the enzymology of infection of Bacillus cereus SPl with the hydroxymethyluracil containing bacteriophage GSW isolated in this laboratory. Following infection, new TTP'ase and hydroxymethyluracil forming enzyme is synthesized, thymidine synthetase is inhibited and some host cell synthetic apparatus is used for phage replication. The control mechanisms of phage replication has been investigated.